sync: add AI review pipeline, parallel skill-files fetch, Redis cache improvements

- feat(review): add skill_reviews table, review API endpoints (pending/submit/stats), admin auth
- perf: parallel file fetching in skill-files API (was sequential → timeout)
- fix: handle Date serialization from Redis cache
- fix: align curation batch scripts with current browseReadyFilter

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/web/lib/admin-auth.ts

@@ -0,0 +1,46 @@
+import { type NextRequest, NextResponse } from 'next/server';
+import { auth } from '@/lib/auth';
+import { createDb, userQueries } from '@skillhub/db';
+
+/**
+ * Check if the current request is from an admin user.
+ * Supports two auth methods:
+ *   1. API key via Authorization: Bearer <REVIEW_API_KEY> header (for automation/scripts)
+ *   2. Session-based admin check (for dashboard)
+ *
+ * Pass the request object to enable API key auth.
+ * Returns the user on success, or a NextResponse error to return early.
+ */
+export async function requireAdmin(request?: NextRequest): Promise<
+  | { authorized: true; username: string }
+  | { authorized: false; response: NextResponse }
+> {
+  // Check API key auth first (for automation/scripting)
+  if (request) {
+    const authHeader = request.headers.get('authorization');
+    const apiKey = process.env.REVIEW_API_KEY;
+    if (apiKey && authHeader === `Bearer ${apiKey}`) {
+      return { authorized: true, username: 'api-key' };
+    }
+  }
+
+  // Fall back to session auth
+  const session = await auth();
+  if (!session?.user?.githubId) {
+    return {
+      authorized: false,
+      response: NextResponse.json({ error: 'Unauthorized' }, { status: 401 }),
+    };
+  }
+
+  const db = createDb();
+  const user = await userQueries.getByGithubId(db, session.user.githubId);
+  if (!user?.isAdmin) {
+    return {
+      authorized: false,
+      response: NextResponse.json({ error: 'Admin access required' }, { status: 403 }),
+    };
+  }
+
+  return { authorized: true, username: user.username };
+}